The invention generally relates to fluid delivery systems used to infuse parenteral fluids to patients intravenously and more particularly, to a mounting linkage for mounting a pumping mechanism.
Physicians and other medical personnel apply fluid infusion therapy to treat various medical complications in patients. For safety reasons and in order to achieve optimal results, it is desirable to infuse parenteral fluid in accurate amounts as prescribed by the physician and in a controlled fashion.
Over the years, various devices and methods have been developed to improve the infusion of fluids in a controlled and more accurate fashion. One type of infusion device is a peristaltic pump that acts on a portion of the tube carrying fluid between the fluid reservoir and the patient. More specifically, a linear-type peristaltic pump sequentially occludes adjacent segments of flexible tubing in a wave-like fashion to create a moving zone of occlusion and force fluid through the tubing. Operation of such a pump typically involves the mechanical operation of a peristaltic pumping mechanism on a flexible tubing positioned between the pumping mechanism and a platen or rigid base and a drive mechanism for driving the pumping mechanism. The pumping mechanism typically comprises a series of pumping devices (fingers) that are driven by a series of drive cams that are mounted on a rotating cam shaft, the cam shaft being coupled to a drive mechanism such as a step-motor. The pumping devices are received in a guide device that confines the movement of the pumping devices to a linear movement against the tubing. The speed of the drive mechanism may be adjusted to achieve a desired volumetric flow rate.
A force limited type of peristaltic pump has a biasing means such as a spring for limiting the force exerted by the pumping devices on the tubing. The pumping devices of a linear peristaltic pump move the same amount in their reciprocal, linear pumping action. The spring permits relative motion between the tubing and the pumping devices so that the force the pumping devices are able to exert on the tubing is kept at a predetermined maximum, which is proportional to the spring force. In one configuration, the pumping mechanism is held in a fixed position and the tubing is placed between the mechanism and a rigid platen, the platen being biased by a spring or springs towards the pumping mechanism. The tubing is placed between the platen and the pumping mechanism. If the compressive force supplied by the moving pumping devices against the tubing exceeds a predetermined threshold established by the springs, the springs yield and allow the platen to be displaced in the direction of such compressive force ensuring that the compressive force remains at the predetermined constant.
The above spring-biased platen approach is not practical in the case where a pumping segment is used that has its own built in platen already coupled to a fluid conduit segment for receiving the pumping devices, and the segment is rigidly mounted in an external position on the pump. In such a case, the pumping devices may be biased towards the tubing so that they may move away from the tubing and platen if the force they exert should exceed the maximum.
However, an important consideration in the mounting of the peristaltic pumping devices, the platen, and the biasing means is keeping a predetermined orientation between the devices when they must move relative to each other to limit the force applied to the tubing. For example, the peristaltic fingers of a linear peristaltic pump are typically mounted in a perpendicular orientation to the tubing to be operated upon and the platen. The platen is typically parallel to the tubing. In the case where the spring-loaded platen must move to relieve the force applied by the fingers, it should do so while remaining parallel to the tubing and perpendicular to the fingers. Likewise in the case where the peristaltic fingers are spring-loaded and must retract from the tubing, they should do so while remaining perpendicular to that tubing so that the correct pumping action continues to occur.
A further consideration in the design of a force limited system is immunity to agents that may interfere with the proper functioning of the force limiting mechanism. In the case where parenteral or other fluids may enter the spaces between the peristaltic fingers or their guides, this fluid may bind the fingers together or to their guides and prevent them from properly moving through the guides. If the mechanism is constructed so that the mechanism can still function partially, it may lift off of the tubing and a free flow condition may result. Such a condition is not desirable. Consequently, it is desirable that the peristaltic pump include a mechanism that prevents unregulated free flow of parenteral fluid from being introduced to the patient.
Hence, those skilled in the art have recognized the need for a mounting mechanism or linkage for use with a peristaltic-type infusion pump that maintains a predetermined orientation between the pumping devices, the tubing and the platen during the times when relative motion occurs between them in force limiting and other operational situations. In addition, those skilled in the art have also recognized the need for a mounting linkage that also prevents free flow through the pumping segment conduit in the event that an outside agent interferes with the proper motion of the pumping devices against the conduit. The present invention fulfills these and other needs.